Exhaust purge device for gas internal combustion engine

ABSTRACT

An object of the present invention is to provide a starting device for a gas internal combustion engine whereby non-combusted gas accumulating in the gas internal combustion engine and an exhaust channel is discharged during ignition startup of the gas engine and abnormal combustion is prevented so as to improve safety, breakage prevention, durability and reliability. An exhaust purge device for a gas internal combustion engine  1  which operates using flammable gas as fuel includes an exhaust channel  16  forming an exhaust channel of the gas internal combustion engine  1,  a blast pipe  71  connected to an upstream portion of the exhaust pipe at one end, an exhaust purge fan  7  connected to another end of the blast pipe  71  and configured to send ambient air to the exhaust channel  16,  and a control device  2  for performing a control to drive the exhaust purge fan  7.  The control device  2  includes: a purge-fan operation determination part  24  configured to determine whether the exhaust purge fan  7  has been operated; and a purge-fan operation command part  28  configured to operate the exhaust purge fan for a set time if it is determined that the exhaust purge fan has not been operated.

TECHNICAL FIELD

The present invention relates to an exhaust purge device for aprecombustion-chamber type lean premixed gas internal combustion engine,for discharging gas accumulating in an exhaust channel before startup ofthe gas internal combustion engine.

BACKGROUND ART

In a precombustion-chamber type lean premixed gas internal combustionengine (hereinafter, referred to in short as a gas engine), there is astarting method adopting slow air turning, in which compressed air (notcontaining fuel gas) is introduced into cylinders to rotate a gas enginebefore starting an air starting device, for the purpose of checking theinside of the cylinders, securing lubrication of the sliding surfaces ofthe cylinders and pistons that slide inside the cylinders, and reducingthe preparation work before starting.

In a gas internal combustion engine that performs slow air turning,compressed air that is used during slow air turning and until startup ofthe engine using compressed air (not containing fuel gas) performedsubsequently to slow air turning performs the role of exhaust purgebefore startup of the gas engine.

However, to secure supply and safety of the fuel gas for the gas engine,a variety of devices, valves, and the like are provided, from whichunpredictable leakage of the fuel gas may occur.

Fuel gas having leaked from the above devices, valves, and the like mayflow to and accumulate in each of the gas engine, an exhaust channel,and the like. If the gas engine is switched to fuel-gas ignition startupunder such a condition, the accumulating fuel gas undergoes abnormalcombustion and damages the gas engine, the exhaust channel, and thelike.

Patent Document 1 discloses performing a dry-air injecting step ofinjecting dry air into an intake channel and a cranking step of ignitingand combusting air-fuel mixture with a spark plug and starting rotationof an output shaft of a gas engine after the dry-air injecting step.

As a result, when the gas engine is started, dry air is injected into anair-supply channel before operation of the spark plug, which reduces theabsolute humidity inside the intake channel.

Thus, when the spark plug operates for the first time after startup, airwith low humidity is supplied into a combustion chamber.

Accordingly, the surface of electrodes of the spark plug is less likelyto get moist, which makes it possible to maintain good insulationresistance between the electrodes, so that the spark plug generatessparks normally and misfire is prevented.

Further, in Patent Document 1, pre-purge, which is to dischargeremaining gas in a combustion chamber to the outside via the exhaustchannel, is performed. At this time, the first injector, the secondinjector, and the spark plug are maintained to be shut down. Aninjection switch valve closes and a starter inlet valve opens. As aresult, a starter motor starts to operate and a flywheel is driven torotate together with an output shaft. Then, the pistons reciprocatewithout the air-fuel mixture undergoing ignition combustion. In thisway, intake valves and exhaust valves are driven by the output shaft,performing opening/closing motion in accordance with the stroke of thepistons.

As the reciprocating motion of the pistons is repeated, the remaininggas in the combustion chamber is forced out to the exhaust channel.Instead, dry air is supplied to a main combustion chamber and aprecombustion chamber from the intake channel.

In this way, it is possible to ventilate the inside of the maincombustion chamber and the precombustion chamber with dry air, whichmakes it possible to prevent non-combusted gas or soot from beingincorporated into air-fuel mixture when the air-fuel mixture undergoesignition combustion for the first time upon startup.

The reciprocating motion of the pistons is repeated a certain number oftimes that is sufficiently large to discharge gas from the maincombustion chamber and the precombustion chamber and that issufficiently small so that air in the supply-air channel does notcompletely pass through the main combustion chamber.

CITED REFERENCES Patent Literature

Patent Document 1: 2012-202376A

SUMMARY Problems to be Solved

However, according to Patent Document 1, the second dry-air injectingstep is performed after a pre-purge step of reciprocating the pistonswithout performing ignition combustion with the air-fuel mixture todischarge the remaining gas in the main combustion chamber to theoutside from the exhaust channel, and before the cranking step. In thisway, dry air is injected again into the supply-air channel. Thus, eventhough the pre-purge step is performed, when the spark plug operates forthe first time after startup, it is possible to prevent air with highhumidity from being supplied into the combustion chamber.

In the pre-purge step, in order to discharge the remaining gas in thecombustion chamber to the exhaust channel, the engine cycle is repeateda certain number of times that is sufficiently large to discharge gasfrom the main combustion chamber and the precombustion chamber and thatis sufficiently small so that air in the supply-air channel does notcompletely pass through the main combustion chamber.

Thus, while it is possible to discharge gas from the main combustionchamber and the precombustion chamber, it is not possible to dischargethe gas accumulating in the exhaust channel completely, and thus it isnot possible to prevent abnormal combustion in the exhaust channelduring fuel-gas ignition operation of the gas engine.

Further, the second dry-air injecting step is to dry the inside of thesupply-air channel to prevent the spark plug of the combustion chamberfrom getting moist.

Thus, non-combusted gas is accumulating in the gas engine and theexhaust channel, and thus it may not be possible to prevent abnormalcombustion when startup of the gas engine is started by the spark plug.

The present invention was made in view of the above issues, and anobject of the present invention is to provide a starting device for agas engine whereby non-combusted gas accumulating in the gas engine andan exhaust channel is discharged before ignition startup of the gasengine and abnormal combustion during ignition startup is prevented soas to improve safety, breakage prevention, durability and reliability.

Solution to the Problems

To achieve the above object, the present invention provides an exhaustpurge device for a gas internal combustion engine that operates usingflammable gas as fuel. The exhaust purge device includes: an exhaustpath connected to an exhaust collecting pipe of the gas internalcombustion engine so as to form an exhaust channel; a blast pipeconnected to an upstream portion of the exhaust pipe at one end; anexhaust purge fan connected to another end of the blast pipe andconfigured to send ambient air to the exhaust channel; and a controldevice for performing a control to drive the exhaust purge fan.

The control device includes: a purge-fan operation determination partconfigured to determine whether an exhaust purge fan has been operatedduring a previous shutdown; and a purge-fan operation command partconfigured to operate the purge fan for a set time which is set inadvance upon next startup of the gas internal combustion engine if thepurge-fan operation determination part determines that the exhaust purgefan has not been operated during the previous shutdown.

According to the above invention, the exhaust purge fan is driven forthe set time either after shutdown or immediately before startup of thegas engine to discharge non-combusted gas accumulating in the exhaustchannel, which makes it possible to prevent abnormal combustion and toimprove reliability upon startup of the gas engine.

Further, preferably in the present invention, the control device mayinclude a set-time varying device configured to make a set value of theset time variable.

Further, preferably in the present invention, the set time becomeslonger with an increase in a capacity forming the exhaust channel.

According to the above invention, on the exhaust side of the gas engine,an exhaust-gas purification device such as a denitration device, a PMfilter, and an oxidation catalyst is disposed depending on the setspecification of the gas engine.

The capacity of the exhaust channel varies depending on the setspecification of the exhaust-gas purification device.

Thus, since the operation time of the exhaust purge fan for causing theambient air to flow through the exhaust channel can be easily operatedto change to a set time corresponding to the capacity of the exhaustchannel, it is possible to ventilate the exhaust channel adequately andto prevent abnormal combustion in the exhaust channel.

Further, even if the capacity of the exhaust channel varies depending onthe specification of the exhaust-gas purification device disposed in theexhaust channel, the set time can be easily changed by the set-timevarying device, which enables the common use of the control device andto reduce the cost for enabling the common use of a component (controldevice).

Further, preferably in the present invention, the exhaust purge devicemay further include an informing device configured to inform completionof the exhaust purge when the exhaust purge is completed.

According to the above invention, the operator is informed that theexhaust purge has been completed and that the next operation may beperformed, which makes it possible to remind the operator not to performthe next operation during the exhaust purge, and to perform safestarting operation for the gas engine.

Advantageous Effects

According to the above invention, it is possible to provide a startingdevice for a gas internal combustion engine whereby non-combusted gasaccumulating in the gas engine and an exhaust channel is dischargedbefore ignition startup of the gas engine and abnormal combustion duringthe ignition startup is prevented so as to improve safety, breakageprevention, durability and reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic overall configuration diagram of a gas engineimplementing the prevent invention.

FIG. 2 is a schematic configuration diagram of an air starting device ofa gas engine according to one embodiment of the present invention.

FIG. 3 is a configuration diagram of a control device according to oneembodiment of the present invention.

FIG. 4 is an operation flowchart of exhaust purge according to thepresent invention.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings.

It is intended, however, that unless particularly specified, dimensions,materials, shapes, relative positions and the like of componentsdescribed in the embodiments shall be interpreted as illustrative onlyand not limitative of the scope of the present invention.

With reference to FIG. 1, the overall configuration of aprecombustion-chamber type lean premixed gas internal combustion engine(hereinafter, referred to in short as a gas engine) implementing thepresent invention will be described.

The gas engine 1 includes: an air starting device 30 coupled to the gasengine 1 via the first pipe 62; a compressed-air tank 9 for supplyingcompressed air to the air starting device 30; a turbocharger 14 mountedto an exhaust-air collecting pipe 12 of the gas engine 1; an exhaustchannel 16 for discharging to the atmosphere exhaust gas having drivenan exhaust turbine (not illustrated) of the turbocharger 14; an aircleaner 18 for removing dust contained in air that is to be supplied tothe gas engine 1; an air cooler 15 coupled coaxially to the exhaustturbine for compressing intake air from the air cleaner 18 and coolingheated supply air; an exhaust-purge fan 7 for exhaust purge coupled tothe exhaust channel 16 at the downstream side of the turbocharger 14 inthe flow direction of exhaust gas via a blast pipe 71, for blowing airinto the exhaust channel 16; a fuel-gas supply device 17 for supplyingfuel gas to the gas engine 1; and a gas-leakage checking device 8disposed in a fuel-gas supply pipe 89 disposed between the fuel-gassupply device 17 and the supply pipe 13, for checking gas leakage ofsafety shutoff valves.

In the exhaust channel 16, an oxidation catalyst 16 b for oxidizing anddetoxifying carbon monoxide (CO) and hydrocarbon (HC) contained in theexhaust gas, a denitration device 16 c for decomposing nitrogen oxide(NOx) contained in the exhaust gas into harmless nitrogen and water byinjecting ammonia (NH3) and using a catalyst so as to obtain cleanexhaust gas, a PM filter 16 a for removing suspended particulate matterscontained in the exhaust gas (PM: particulate matter), and the like aredisposed in accordance with the required specification of the device.

Thus, depending on the required specification of the exhaust-gaspurification device to be mounted, the channel capacity of the exhaustchannel 16 varies.

Further, 23 is a rotation-speed sensor for measuring the cumulativerotation speed of slow-air turning upon startup of the gas engine.

FIG. 2 is a schematic configuration diagram of the air starting device30. The air starting device 30 includes a control device 2 forcontrolling operation of the air starting device 30, a main air-startingunit 6 which increases the gas engine 1 to a rotation speed for startupof fuel-gas ignition operation, and a compressed-air supply unit 3 forperforming slow-air turning for checking the inside of each cylinder ofthe gas engine 1 and securing lubrication of the sliding surfacesbetween cylinders and pistons in the cylinders before operation of themain air-starting unit 6.

In the present embodiment, the control device 2 is a comprehensivecontrol device which controls the air starting device 30, the exhaustpurge fan 7 for exhaust purge and the gas-leakage checking device 8.

As illustrated in FIG. 3, the control device 2 includes the following inorder to perform exhaust purge: a purge-fan operation determination part24 configured to determine whether the exhaust purge fan 7 has beenoperated during the previous shutdown; a purge-fan operation commandpart 26 for operating the purge fan for a set period of time upon thenext startup, if it is determined that the purge fan 7 has not beenoperated previously by the purge-fan operation determination part 24,and a time-setting device 26 for setting the period of time foroperating the exhaust purge.

The time-setting device 26 includes a time (minute) inputting switch 27of a dial type capable of varying the operation time of exhaust purge inaccordance with the capacity of the exhaust channel upon execution ofexhaust purge.

The main air starting unit 6 includes a main starting valve 61, an airstarting switch 65 (hereinafter, switch is referred to in short as S/W)that operates the main starting valve 61 via the control device 2, astarting electromagnetic valve 64 that opens the main starting valve 61via the first pipe 62 with compressed air from the compressed-air tank 9when the air starting S/W 65 is switched on, and a compressed-airintroduction unit 5 that introduces compressed air into each cylinderaccording to the order of ignition timing of the gas engine 1, thecompressed air being supplied by opening the main starting valve 61.

The opened main starting valve 61 sends the compressed air for operationfor air startup toward the compressed-air introduction unit 5 via thefirst pipe 62.

The compressed-air introduction unit 5 includes: a starting-pipe controlvalve 51 which distributes pilot air to each cylinder of the gas engine1 according to the order of ignition timing of the gas engine 1; astarting valve 52 that is mounted to a cylinder head 11 of the gasengine 1 and opened by pilot air from the starting-pipe control valve51; the fourth pilot air pipe 56 coupling the starting-pipe controlvalve 51 and the starting valve 52; the third pilot air pipe 55 that isbranched from the second pipe 63 and introduces pilot air to thestarting-pipe control valve 51; and an interlock valve 53 disposed inthe third pilot air pipe 55 for safety check that afitting-and-disengaging device of an engine turning device is removedbetween the main starting valve 61 and the starting valve 52.

Here, a slow-air-turning main starting valve 31 has a structure suchthat the compressed air from the third pipe 37 is not discharged to theatmosphere from the slow-air-turning main starting valve 31 duringoperation of the main starting valve 61 while operation of theslow-air-turning main starting valve 31 is halted.

Accordingly, when the air starting S/W 65 is switched on, the startingelectromagnetic valve 64 opens. The main starting valve 61 is opened bythe compressed air from the starting electromagnetic valve 64. Thecompressed air passes through the first pipe 62, the main starting valve61, the second pipe 63, the third pilot air pipe 55, and the interlockvalve 53 in this order, thereby reaching the starting-pipe control valve51 in the end. The starting-pipe control valve 51 sends pilot air to thestarting valve 52 mounted to a cylinder that has reached the ignitiontiming of the time of the previous shutdown of the gas engine 1.

The starting valve 52 opens, and the compressed air from the second pipe63 is introduced into the cylinder from the starting valve 52.

The piston in the cylinder is pressed by the compressed air, and the gasengine 1 starts rotation.

When the gas engine 1 reaches a predetermined rotation speed, the gasengine 1 starts operation by fuel-gas ignition.

Once the gas engine 1 starts operating by fuel-gas ignition, the controldevice 2 closes the starting electromagnetic valve 64, as well ashalting supply of the compressed air to the main starting valve 61 andclosing the main starting valve 61.

When the main starting valve 61 closes, the compressed air accumulatingin the second pipe 63 and the third pilot air pipe 55 is discharged tothe atmosphere from the main starting valve 61 via a switch valve 32that is normally open.

The main starting valve 61 has a structure such that the compressed airin the starting circuit is discharged to the atmosphere when operationof the main starting valve 61 is halted, because compressed airremaining in the compressed-air circuit of the compressed-airintroduction unit 5 generates internal resistance of the gas engine 1during fuel-gas operation.

Before the main air starting unit 6 is started, slow air turning isperformed to check the inside of each cylinder of the gas engine 1,lubricate the piston ring and the cylinder liner inside the cylinder,and to check safety around the combustion chamber.

In the present invention, in addition to the above reasons, in a casewhere shutdown is caused by occurrence of an unpredictable event (e.g.emergency stop of the gas engine 1 due to loss of control power or thelike) and exhaust purge is not performed on the exhaust channel 16 afterthe shutdown, fuel gas remaining in the fuel gas supply pipe 89 flowsout to and accumulates in the gas engine 1 and the exhaust channel 16.In a case where non-combusted fuel gas has accumulated in the gas engine1 and the exhaust channel 16 disposed on the downstream side of the gasengine 1, such non-combusted fuel gas is discharged in order to preventoccurrence of abnormal combustion due to the accumulating fuel gasduring fuel-gas ignition operation of the gas engine 1.

With reference to FIG. 2, the configuration of the compressed-air supplyunit 3 for performing slow air turning will be described.

The compressed-air supply unit 3 includes: the slow-air-turning mainstarting valve 31; a slow-air-turning electromagnetic valve 34 thatopens the slow-air-turning main starting valve 31 by supplying pilot airto the slow-air-turning main starting valve 31 from the compressed-airtank 9 via the second pilot air pipe 35; the compressed-air introductionunit 5 that introduces the compressed air supplied as theslow-air-turning main starting valve 31 opens into each cylinderaccording to the order of ignition timing of the gas engine 1, anorifice 25 for pressure reduction disposed in the third pipe 37connecting the second pipe 63 and the slow-air-turning main startingvalve 31; a switch valve 32 mounted to the main starting valve 61 toprevent the compressed air from being discharged to the atmosphere fromthe halted main starting valve 61 during operation of theslow-air-turning main starting valve 31, a rotation-speed detection unitwhich detects the number of slow air turning (rotation speed of a crankshaft) of the gas engine 1; and a cumulative rotation-speed settingdevice 21 which is capable of closing the slow-air-turningelectromagnetic valve 34 and varying a set value of the cumulativerotation speed optionally when the cumulative rotation speed of therotation speed detected by the rotation-speed detection unit reaches theset value.

The switch valve 32 is mounted to the downstream side of the mainstarting valve 61, and opened by pilot air introduced by the fifth pilotair pipe 36 branched from the second pilot air pipe 35, so that thecompressed air is not discharged to the atmosphere from the mainstarting valve 61 during operation of slow air turning.

Accordingly, while the slow air turning is performed, the compressed airin the operation circuit of the slow air turning is prevented from beingdischarged to the atmosphere from the main starting valve 61, whichmakes it possible to perform operation of the slow air turning.

Once the gas engine 1 starts to operate by fuel, the operation of themain starting valve 61 stops, and thereby the compressed air in theoperation circuit of the slow air turning is discharged to theatmosphere from the main starting valve 61 to prevent the compressed airfrom becoming internal resistance of the gas engine 1.

Performing slow air turning makes it possible to eliminate remaining gasin the gas engine 1 and the exhaust channel 16.

However, various exhaust-gas purification devices are disposed in theexhaust channel 16 in view of prevention of environmental pollution.

As described above, the exhaust-gas purification devices include, forinstance, the oxidation catalyst 16 b, the denitration device 16 c, thePM filter (PM; particulate matter) 16 a for purifying exhaust gas, andthe like, arranged in accordance with the required specification of thedevice.

The specification of the exhaust-gas purification devices is varieddepending on the characteristics of a usage area, demand of the client,or the like, and thus the capacity inside the exhaust channel 16 alsovaries.

In view of this, varying a set value of the cumulative rotation speed ofslow air turning in accordance with the capacity inside the exhaustchannel 16 makes it possible to reduce the cost by sharing the controldevice 2, as well as discharging air (which may contain fuel gas) in thegas engine 1 and the exhaust channel 16.

Further, according to the present invention, exhaust purge is operatedbefore execution of the above slow air turning.

The exhaust purge includes the exhaust purge fan 7, the blast pipe 71connected to the exhaust purge fan 7 at one end and to the exhaustchannel 16 at the downstream side of the turbocharger 14 with respect tothe exhaust turbine at the other end, the time-setting device 26provided for the control device 2, and a pilot lamp 29 which is aninforming device for informing an operator of completion of exhaustpurge, from a signal from the control device 2.

The time-setting device 26 includes the time (minute) inputting switch27 of a dial type for setting the operation time of exhaust purge.

The set time of the time setting device 26 can be set to be long if thecapacity of the exhaust channel is large, and to be short if thecapacity is small.

Further, while the pilot lamp 29 is used as an informing device in thepresent embodiment, a buzzer may be used instead, or both of a buzzerand the pilot lamp 29 may be used together.

In this case, the operator is informed that the exhaust purge has beencompleted and that the next operation may be performed, which makes itpossible to remind the operator securely not to perform the nextoperation during the exhaust purge, and to perform safe startingoperation for the gas engine.

With reference to FIG. 4, the control for performing exhaust purge willbe described.

The process starts from step S1, and in step S2, an operator confirmswhether the set time of exhaust purge is set corresponding to thecapacity of the exhaust channel.

If the set time is not corresponding to the capacity of the exhaustchannel, the time inputting S/W 27 of the time-setting device 26 isoperated to correct the set time.

In step S3, the operator issues a startup preparation command of anengine (a starting switch 65 is turned on) in order to start the gasengine 1.

In step S4, the control device 2 confirms whether exhaust purge has beenperformed on the exhaust channel 16 during the previous shutdown of thegas engine 1.

If exhaust purge has not been performed, NO is selected and the processadvances to step S5.

In step S5, the control device 2 operates the exhaust purge fan 7 ofexhaust purge for a set time to discharge air (that may contain fuelgas) in the exhaust channel 16 with the ambient air.

The operation time is determined in accordance with the capacity of theexhaust channel that varies depending on the arrangement specificationof the various exhaust gas purification devices disposed in the exhaustchannel 16.

After performing the exhaust purge for a predetermined period, theprocess advances to step S6, and the control device 2 informs (confirms)completion of the exhaust purge with the pilot lamp 29, which is aninforming device.

The operator can confirm that the exhaust purge is completed and thatthe next operation can be performed.

The control device 2 is configured such that air startup (slow airturning), which is the next step, cannot be performed unless completionof the exhaust purge is confirmed by the control device 2.

In step S4, if exhaust purge has been performed on the exhaust channel16 during the previous shutdown of the gas engine 1, YES is selected andthe process advances to step S25.

Step 6 and following steps are as described above, and thus notdescribed in detail.

In this way, in a case where shutdown is caused by some reason (e.g.emergency stop of the gas engine 1 due to loss of control power or thelike) and exhaust purge is not performed on the exhaust channel 16 afterthe shutdown, fuel gas remaining in the fuel gas supply pipe 89 flowsout to and accumulates in the gas engine 1 and the exhaust channel 16.

Upon startup, it is possible to prevent abnormal combustion in theexhaust channel 16 by automatically performing exhaust purge that hasfailed to be performed during the previous shutdown of the gas engine 1.

It is also possible to prevent unnecessary operational errors because itis possible to confirm completion of the exhaust purge with the pilotlump 29 easily, which enables the operator to determine normal operationof the control device 2.

In the present embodiment, it is confirmed whether exhaust purge hasbeen performed during the previous shutdown of the gas engine 1 (step S4in FIG. 4), and exhaust purge is not performed before startup of the gasengine 1 if exhaust purge has been performed. However, exhaust purgebefore startup may be a requirement.

With the execution of exhaust purge before startup being a requirement,even if temporary deformation (elastic deformation) or the like occursto a seal portion of a number of valves due to an earthquake or thelike, and fuel-gas leaks from the deformed part to accumulate in theexhaust channel 16 while the gas engine 1 is halted, it is possible toimprove safety with respect to abnormal combustion in the exhaustchannel 16 even further.

In this way, it is possible to provide a starting device for a gasinternal combustion engine whereby non-combusted gas possiblyaccumulating in the gas engine 1 and the exhaust channel 16 isdischarged upon ignition startup of the gas engine 1 and abnormalcombustion is prevented so as to improve safety, breakage prevention,durability and reliability of the gas engine 1.

INDUSTRIAL APPLICABILITY

The present invention is suitably applied to a starting device for a gasinternal combustion engine equipped with a slow air turning device thatis operated before startup of an internal combustion engine including anair starting device.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Gas internal combustion engine (precombustion-chamber type lean    premixed gas internal combustion engine)-   2 Control device-   3 Compressed-air supply unit-   5 Compressed-air introduction unit-   6 Main air starting unit-   7 Exhaust purge fan-   11 Cylinder head-   12 Exhaust-collecting pipe-   13 Supply pipe-   16 Exhaust channel-   17 Fuel-gas supply device-   24 Purge-fan operation determination part-   26 Time setting device-   27 Time inputting S/W-   28 Purge-fan operation command part-   30 Air starting device-   31 Slow-air-turning main starting valve-   32 Switch valve-   51 Starting pipe control valve-   52 Starting valve-   61 Main starting valve-   71 Blast pipe

1. An exhaust purge device for a gas internal combustion engine whichoperates using flammable gas as fuel, the exhaust purge devicecomprising: an exhaust pipe connected to an exhaust collecting pipe ofthe gas internal combustion engine so as to form an exhaust channel; ablast pipe connected to an upstream portion of the exhaust pipe at oneend; an exhaust purge fan connected to another end of the blast pipe andconfigured to send ambient air to the exhaust channel; and a controldevice for performing a control to drive the exhaust purge fan, whereinthe control device includes: a purge-fan operation determination partconfigured to determine whether the exhaust purge fan has been operatedduring a previous shutdown; and a purge-fan operation command partconfigured to operate the purge fan for a set time which is set inadvance upon next startup of the gas internal combustion engine if thepurge-fan operation determination part determines that the exhaust purgefan has not been operated during the previous shutdown.
 2. The exhaustpurge device for a gas internal combustion engine according to claim 1,wherein the control device includes a set-time varying device configuredto make a set value of the set time variable.
 3. The exhaust purgedevice for a gas internal combustion engine according to claim 1 or 2,wherein the set time becomes longer with an increase in a capacityforming the exhaust channel.
 4. The exhaust purge device for a gasinternal combustion engine according to any one of claims 1 to 3,further including an informing device configured to inform completion ofthe exhaust purge when the exhaust purge is completed.